the most simple way with good results is to dig a hole as big as the amount of potting soil you want to carry, fill it with potting soil, and plant your seedlings that you have already started in cups. you can also amend the existing soil with potting soil. Living in chicago, you might want to top your plants to keep them short. I am saying this because of the population density of your area and IMO this increases the chances of someone finding your plants.